1. Field of the Invention
The invention relates to a carbon fiber, and more specifically to an activated carbon fiber for fabricating a supercapacitor electrode and its precursor material.
2. Description of the Related Art
Among precursor materials for carbon fibers, polyacrylonitrile (PAN) has a great potential due to its high molecular orientation, high melting point, and high carbon yield (exceeding 45%). After a pre-heating treatment, a high-order ladder-typed oxidized PAN fiber structure is formed, with high thermal stability. During activation, the main molecular chain of PAN remains unchanged, without cleavage, such that an activated carbon fiber with excellent quality is prepared.
Currently, a lithium secondary battery is the main power energy source due to its high energy density. Carbon is the key material for the negative electrode thereof, for example, mesocarbon microbeads (MCMB) or graphite fibers (or powders). However, the lithium secondary battery cannot provide a high-power output because of its electrode structure, limiting the applications for power tools and electric vehicles (EV). High-power output can be achieved with a combination of supercapacitor and battery. Generally, activated carbon materials with a high surface area, a high porosity, and a high electric conductivity can be utilized as the electrode material of the supercapacitor. Further, such properties can be improved by formation of nano carbon materials. However, when nano carbon material is utilized to prepare an electrode, a great quantity of binder is required, resulting in low energy density. Finer carbon fibers can solve the above problem.